encrypt credentials to create datasource - PowerShell

I'm trying to automate gateway data source management using PowerShell. First I need to encrypt credentials. Here is my PowerShell script to do this;

$segmentLength = 85
$encryptedLength = 128
$plaintTxt = '{"credentialData":[{"value":"'+$Username+'","name":"username"},{"value":"'+$Password+'","name":"password"}]}'
$rsa = New-Object System.Security.Cryptography.RSACryptoServiceProvider ($encryptedLength * 8)
$parameters = $rsa.ExportParameters($false)
$parameters.Exponent = [System.Convert]::FromBase64String($GatewayExponent)
$parameters.Modulus = [System.Convert]::FromBase64String($GatewayModulus)
$rsa.ImportParameters($parameters)
$plainTextArray = [System.Text.Encoding]::UTF8.GetBytes($plaintTxt)    
$hasIncompleteSegment = $plainTextArray.Length % $segmentLength -ne 0

$segmentNumber = If (-not $hasIncompleteSegment) {[int]($plainTextArray.Length / $segmentLength)} Else {[int]($plainTextArray.Length / $segmentLength) + 1}
$encryptedData = [System.Byte[]]::CreateInstance([System.Byte],$segmentNumber * $encryptedLength)
[int]$encryptedDataPosition = 0;

For ($i=0; $i -lt $segmentNumber; $i++) {
    $lengthToCopy = If ($i -eq ($segmentNumber - 1) -and $hasIncompleteSegment) {$plainTextArray.Length % $segmentLength} Else {$segmentLength}
    $segment = [System.Byte[]]::CreateInstance([System.Byte],$lengthToCopy)
    [System.Array]::Copy($plainTextArray,$i*$segmentLength,$segment,0,$lengthToCopy)
    $segmentEncryptedResult = $rsa.Encrypt($segment, $true)
    [System.Array]::Copy($segmentEncryptedResult,0,$encryptedData,$encryptedDataPosition,$segmentEncryptedResult.Length)
    $encryptedDataPosition += $segmentEncryptedResult.Length;
}

return [System.Convert]::ToBase64String($encryptedData)

The solution described on this page stopped working - on the end of 2019

We're receiving the error that the
"Destination array was not long enough. Check destIndex and length, and the array's lower bounds"
on the line "Array.Copy(segmentEncryptedResult, 0, encryptedData, encryptedDataPosition, segmentEncryptedResult.Length);"

Do you have any fix writing in PowerShell? I have found sth in cs: microsoft/PowerBI-CSharp@83ba689

I will be apricated for any hint. Thanks!